1. Field of the Invention
The present invention concerns a novel process for the synthesis of vanadium oxide V.sub.6 O.sub.13 by reduction of V.sub.2 O.sub.5 in the presence of a mixture of reducing gas.
2. Discussion of the Background
Different processes for the synthesis of vanadium oxide V.sub.6 O.sub.13 have already been proposed. For example, it is possible to reduce V.sub.2 O.sub.5 by utilizing metallic vanadium, at high temperature and with a very long contact time, from two to three days.
It is also possible to foresee a reduction by NH.sub.3 or hydrogen. These different processes are long and complicated, since, for example, the synthesis by reduction to metallic vanadium requires a very strong static vaccum. Furthermore, they have the drawback of supplying V.sub.6 O.sub.12 in the form of needles.
One of the concerned applications for vanadium oxide disclosed according to the present invention is the obtention of positive electrodes for a lithium generator and the electrolyte of which is a lithium salt in solution in a macro-molecular material.
Such a generator is, for example, disclosed in European Pat. No. 1399. In this type of generator, it is foreseen to utilize V.sub.6 O.sub.13 as insertion material adapted for lithium atoms to be inserted. In order to obtain good performances for the reaction, the applicants have discovered that it was preferable that the vanadium oxide be present in the forms of grains, i.e. having a morphology entirely different to that obtained with the reduction methods utilizing metallic vanadium, NH.sub.3 or hydrogen.
On the other hand, in order to obtain such positive electrodes, it is preferable to have as pure a product as possible, and, in particular, a product that is quasi-free of V.sub.2 O.sub.5 ; this latter, when it is present in large quantities in the electrode material, distorts the discharge curves and, in particular, provokes a sharp variation of the discharge voltage.